1. Field of the Invention
The invention relates in general to a method for frame processing and an apparatus therefor, and more particularly to a method for frame processing in a liquid crystal display panel and an apparatus therefor.
2. Description of the Related Art
There is rapid advancement in the field of display technology. For example, traditional cathode ray tube (CRT) monitors are relatively large and emit a high amount of radiation. They are gradually being replaced by liquid crystal display (LCD) monitors that have the advantages of lower radiation, lower power consumption, and smaller size.
A display panel is composed of multiple pixels in the form of a matrix. When a frame is displayed on a monitor, pixels receive their corresponding pixel-voltage sequentially, according to the pixel-data. The pixel voltage varies according to the pixel data, and according to the variations, frames can be refreshed of different frames can be displayed. If the frame's refresh rate is greater than a certain amount, then what the eyes perceive, due to the effect of temporary visual retention, is not a number of frames flipping through the screen but a continuous display. A greater refresh rate provides a more continuous display, and thereby less flickering that causes discomfort to the eyes. The refresh rate of modern monitors is greater than 60 Hz, which means at least 60 frames are displayed per second.
A pixel of an LCD monitor is the combination of a front plate, a rear plate, and a liquid crystal layer between the front and rear plates. The space between the plates is filled with a number of liquid crystal molecules to form the liquid crystal layer. There are electrodes on both plates, and when applied voltages on the electrodes reaches a certain level, a voltage is formed across the front and rear plates and influences the arrangement of the liquid crystal molecules. Arrangement of the liquid crystal molecules affects the ratio of light permissible through the pixel (light transmissivity). Light transmissivity determines the luminosity of a pixel. The higher light transmissivity is the more luminous a pixel can be. Therefore, by controlling the voltage across the front and rear plates, different luminosity can be assigned to the pixels on the panel.
FIGS. 1A and 1B show pixel luminosity changes according to the pixel voltage. When the input pixel voltage changes, it requires a response time for the theoretical luminosity level to be achieved due to the physical property of the liquid crystal molecules. In FIG. 1A, the input pixel voltage rises from V1 to V2 when frame f2 is displayed. Theoretically, the expected luminosity level of the pixel should be achieved right at the start of the display of f2; the pixel luminosity B1, which corresponds to pixel voltage V1, should rise immediately to the luminosity level B2, which corresponds to pixel voltage V2, shown by the dotted line in FIG. 1B. In reality, it takes a while for the liquid crystal molecules to adapt to their new positions. Therefore, the expected luminosity cannot be achieved until after a certain amount of response time, during which time the crystal liquid molecules are becoming properly aligned. In FIG. 1B, the pixel voltage was changed at the start of f2, but the pixel luminosity cannot reach B2 until f5 is displayed. When a pixel's pixel voltage changes from V1 to V2, the time required to change the pixel luminosity from B1 to B2 is called the pixel response rate. The longer the response time of the liquid crystal molecules, the slower the response rate. Between frames f2 and f5, the actual luminosity is less than the expected value, shown as the area of diagonal lines. The quality of the LCD is thereby degraded. Therefore, the task of how to increase the response rate and decrease the area shown by the diagonal lines when the input pixel voltage changes is important to manufacturers of LCD monitors.
FIGS. 2A and 2B show the traditional technique used to increase the pixel response rate, called overdrive. The traditional technique works by supplying a pixel voltage higher than required in order to shorten the length of time required to build up the voltage across the plate and rear plates, thus increasing the pixel response rate when the pixel luminosity needs to be increased. For example, in FIG. 2A, the input pixel voltage needs to be raised from V1 to V2 in order to raise the luminosity from B1 to B2 when frame f2 is displayed. In order to increase the response rate, a pixel voltage V3, which is higher than V2, is input when frame f2 is displayed. Pixel voltage V3 is called the overdrive voltage herein. By inputting the overdrive voltage, the response rate can be enhanced. The shaded area with diagonal lines in FIG. 2B is smaller than the corresponding shaded area in FIG. 1B. The difference between the pixel's actual luminosity and expected luminosity can be decreased by the use of overdrive voltage.
For the same reason, when the pixel luminosity needs to be decreased, a lower than usual pixel voltage is input, shortening the time required to reduce the voltage across the front and rear plates.
Although the traditional overdrive can increase the pixel response rate, it can only provide limited improvement for the difference between the actual and the expected luminosities.